1. Field of the Invention
This invention relates to an image formation apparatus such as a copying apparatus or an information recording apparatus for high-frequency-wave-fixing an an unfixed image to thereby form an image.
2. Description of the Prior Art
Fixing devices using high-frequency electromagnetic waves to effect fixation are disclosed in Japanese Patent Publication No. 38171/1974, Japanese Laid-open Patent Application No. 20039/1977 and Japanese Patent Publication No. 10865/1979.
High-frequency wave heating and fixing devices are excellent in eliminating the following disadvantages in the so-called extraneous heating and fixation. That is, they are devices which reduce the wait time until a condition necessary for fixation is reached, eliminate the danger of fire or the like which may occur when a recording medium such as paper stagnates in the fixing area for some reason, and prevent wrinkling of the recording medium and disturbance of the image thereon.
A conventional high-frequency wave heating and fixing device will now be described in greater detail. This device utilizes a hollow microwave guide tube as high-frequency wave generating means, and it is structurally formed as shown in FIG. 1A (prior art) of the accompanying drawings and its cross-section is as shown in FIG. 1B of the accompanying drawings. In FIG. 1, reference numeral 1 designates a microwave oscillator which generates a microwave having a component of electric field in the direction 2 of transmission. A magnetron is used in this microwave oscillator 1. Designated by 3 is a hollow waveguide tube having a rectangular shape through which microwaves are transmitted in the direction of arrow 2. The waveguide tube 3 is provided in parallel to a recording medium 7. Slits 4 are provided in that surface of the waveguide tube with respect to which the surface of the recording medium 7 opposite to the surface bearing a toner image 6 slides. The microwave emitted outwardly through these slits 4 and applied to the toner and recording medium 7 contributes to fixation. (The fixing phenomenon occurs due chiefly to the self-heating and melting resulting from the absorption of high-frequency electromagnetic wave by the toner.) Reference numeral 5 denotes a cooling device provided perpendicularly to the waveguide tube 3 with the waveguide tube interposed between the cooling device and the microwave oscillator 1 to extinguish the generated microwave energy.
However, in the fixing device of the type in which, as described above, slits are formed in a surface of the microwave guide tube to allow leakage of microwave, the size of the slits must be determined such that an area necessary for a predetermined amount of microwave leakage is secured. Therefore, the output of the microwave generator such as a magnetron must be increased to secure an appropriate microwave energy per unit area and this has led to the bulkiness and increased cost of the device. Also, the utilization efficiency of microwave device has been low and accordingly, the fixing efficiency has not been high.